The invention relates to a process for the manufacture of belting having a single layer central portion and tubular edge portions. A process of this kind is known from the German laid-open document (Offenlegunsschrift) No. 27 18 382 of the same applicants now U.S. Pat. No. 4,174,738.
Belting made in this way is used mainly for safety belts in vehicles. The use of a needle belt weaving loom makes the formation of a row of woven stitching to close one tubular edge necessary. According to the publication cited above, the row of stitching is laid at the edge of the central portion and loops of the row of stitching are drawn into the central portion, so that the stitching row practically disappears into the central portion.
The weft thread insertion needle (called hereinafter "weft needle") must enter twice successively into the same shed formed for the central portion. The sheds are reversed only for the edge part, so that each time, one pick forms the edge part fabric and the next takes up only one of the two outside warp threads and then serves to draw back the edge part to make the tubular edge portion.
It is intended by means of the present invention to increase the rate of weft insertion, in particular, to double it and to do it in such a manner that the row of stitching practically disappears into the belting.
The present invention provides a process for the manufacture of belting having a single layer central portion and two tubular edge portions on a needle belt weaving loom provided with a knitting needle, the process comprising the steps of:
(a) weaving both tubular edge portions in the form of single layer edge parts; PA1 (b) forming stitches at the outer edge of one edge part by means of the knitting needle; PA1 (c) closing both edge parts by weft thread tension to form the tubular edge portions; PA1 (d) drawing loops from the stitches pulled to the edge of the central portion into the central portion by weft thread tension, characterized by the following features: PA1 (e) two weft threads are inserted simultaneously at each pick by means of two weft thread insertion needles; PA1 (f) for anchoring one weft thread at the outer edges of the edge parts a common shed for both weft thread insertion needles is formed at least on the insertion side by the two outer edge warp threads; PA1 (g) for weaving the edge parts between the central portion and the two outer edge warp threads an upper and a lower shed are formed, of which one shed accepts the first weft thread insertion needle which forms the edge fabric, and the other shed the second weft thread insertion needle of which the weft thread binds only with at least one of the two outer edge warp threads; PA1 (h) a loop is drawn by the knitting needle outside one of the edge parts through a loop of at least one of the weft threads to form a stitch; PA1 (i) the two weft threads are positively fed and the length fed of the first weft thread is greater by at least the width of the two edge parts than the length fed of the second weft thread.
Instead of a single weft needle, two are used, which are inserted simultaneously at each pick. By this means the rate of weft insertion is doubled for the same warp speed. This means twice the length of belting in unit time.
The process of making the row of stitching is as follows: one of the two wefts forms the edge fabric while the other takes up one of the two outer warp threads.
The knitting needle is so guided that it draws a loop (one of the weft threads or a catch thread) through a loop of the other weft thread or of both weft threads and forms a stitch. By tension on the second weft thread, which picks up only one of the two outer warp threads, the two edge parts are then closed to form tubular edge portions. As described in the prior publication, from the row of stitching formed at one edge part a loop is drawn into the fabric of the central portion.
The different lengths of the two wefts are taken into account, since only one of them forms the tubular edge portions and must therefore be longer than the other, which forms only the central portion.
The use of two weft needles affords the advantage that only half as many stitches need be formed as with the use of a single weft needle. This results in a thinner row of stitching which can be drawn better and more completely into the fabric than a row of stitching formed by a single weft needle. The belting so formed is thus better protected against wearing out of the stitching.
In the German Offenlegungsschrift No. 21 61 013 a weaving process is described in which two weft needles are used and at one edge of the fabric a row of stitching is formed from one weft thread with an auxiliary thread. In this case however no tubular edge portion is formed; instead both weft threads are taken to the edge of the fabric. This publication therefore gives no information on how to proceed if it is required to form a tubular edge portion by the simultaneous insertion of two weft needles, i.e. when the two weft needles have to perform two very different functions.
According to an embodiment of the present invention weft threads of different thickness can be used. Therefore by skilful combination of weft materials of different thickness belting can be made of qualities which do not correspond to normal commercial thicknesses. The thickness of the belt and the transverse stiffness can be selected at will without changing the weft density by the use of two weft threads of different thickness.
According to a further embodiment of the invention a monofilament yarn can be used for the second weft thread. The second weft thread serves to draw in the single layer edge part to form a tubular edge portion, but does not serve to make the edge part fabric. Monofilament yarns are harder than the normally used multifilament yarns. By weaving with monofilament yarns as weft threads, belts with greater transverse stiffness can therefore be achieved, which is very advantageous for coiling in vehicle safety belt automatic reeling equipment. Monofilament yarns would on the other hand exert a greater rubbing effect on the clothing or body of the user of a safety belt if they projected at the edge of the belt. This is avoided in that the monofilament yarn is used only for making the central portion of the belting and to draw the single layer edge part in, while this is itself woven from a multifilament yarn.
By the use of a relatively stiff monofilament yarn for one of the weft threads a smaller number of wefts per cm of belt length can be woven than by the use of two multifilament yarns of the same thickness as the weft threads. By this means a higher production speed is achieved.
In principle there are various possibilities for forming the row of stitching. The two weft threads can be knitted together or one weft thread can be knitted with a catch thread. In both cases the row of stitching can be protected against drawing out by an additional barrier thread.
If a catch thread is used and a thinner yarn is used for the catch thread than for the weft thread, the thickness of the stitching can be still further reduced.
According to one embodiment of the invention, the catch thread and barrier thread can be fed in by one and the same thread inserter, which reduces the constructional cost of the loom.
The invention relates further to a thread inserter for a needle belt weaving loom for carrying out the process according to the aforementioned embodiment. By means of a single thread inserter, which may have two prong-like extensions, the catch thread and barrier thread can be fed in together.